U.S. patent application number 13/667438 was filed with the patent office on 2013-08-29 for image forming apparatus.
This patent application is currently assigned to FUJI XEROX CO., LTD.. The applicant listed for this patent is FUJI XEROX CO., LTD.. Invention is credited to Atsuyuki KITAMURA, Shuichi NISHIDE, Atsushi OGIHARA, Tetsuji OKAMOTO, Masahiro SATO, Wataru SUZUKI, Koichi WATANABE.
Application Number | 20130223900 13/667438 |
Document ID | / |
Family ID | 49003022 |
Filed Date | 2013-08-29 |
United States Patent
Application |
20130223900 |
Kind Code |
A1 |
WATANABE; Koichi ; et
al. |
August 29, 2013 |
IMAGE FORMING APPARATUS
Abstract
An image forming apparatus includes an image carrier, a transfer
member, a leading end holding member, a trailing end holding
member, a detection unit, and a stopping unit. The trailing end
holding member is disposed so as to be rotatable around the
transfer member such that a gap is formed between the trailing end
holding member and the transfer member. The trailing end holding
member holds a trailing end of the recording medium after a leading
end of the recording medium held by the leading end holding member
has passed through the gap. The detection unit detects whether the
leading end of the recording medium passes through the gap after
the leading end holding member performed a holding operation on the
leading end. The stopping unit stops rotation of the transfer
member when the detection unit detects that the leading end does
not pass through the gap.
Inventors: |
WATANABE; Koichi; (Kanagawa,
JP) ; NISHIDE; Shuichi; (Kanagawa, JP) ;
SUZUKI; Wataru; (Kanagawa, JP) ; OKAMOTO;
Tetsuji; (Kanagawa, JP) ; OGIHARA; Atsushi;
(Kanagawa, JP) ; SATO; Masahiro; (Kanagawa,
JP) ; KITAMURA; Atsuyuki; (Kanagawa, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJI XEROX CO., LTD.; |
|
|
US |
|
|
Assignee: |
FUJI XEROX CO., LTD.
Tokyo
JP
|
Family ID: |
49003022 |
Appl. No.: |
13/667438 |
Filed: |
November 2, 2012 |
Current U.S.
Class: |
399/304 |
Current CPC
Class: |
G03G 15/167 20130101;
G03G 2215/0177 20130101 |
Class at
Publication: |
399/304 |
International
Class: |
G03G 15/01 20060101
G03G015/01 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 23, 2012 |
JP |
2012-037709 |
Claims
1. An image forming apparatus comprising: an image carrier that
carries an image on an outer peripheral surface thereof; a transfer
member disposed such that an outer peripheral surface thereof is in
contact with the outer peripheral surface of the image carrier, the
transfer member transporting a recording medium, the transfer
member transferring the image carried by the image carrier to the
recording medium; a leading end holding member disposed on the
transfer member and holding a leading end of the recording medium
in a transport direction; a trailing end holding member disposed at
a predetermined standby position such that a gap is formed between
the trailing end holding member and the outer peripheral surface of
the transfer member, the trailing end holding member being
rotatable around the transfer member independently of the transfer
member, the trailing end holding member holding a trailing end of
the recording medium in the transport direction after the leading
end of the recording medium in the transport direction held by the
leading end holding member has passed through the gap while the
transfer member rotates; a detection unit that detects whether the
leading end of the recording medium passes through the gap after
the leading end holding member performed a holding operation on the
leading end; and a stopping unit that stops rotation of the
transfer member when the detection unit detects that the leading
end does not pass through the gap.
2. The image forming apparatus according to claim 1, wherein the
trailing end holding member is movable by a force applied to the
trailing end holding member in the transport direction.
3. The image forming apparatus according to claim 2, wherein the
detection unit detects whether the leading end of the recording
medium passes through the gap by detecting a position of the
trailing end holding member.
4. The image forming apparatus according to claim 1, further
comprising: a contact member that is movable and disposed upstream
of the standby position in the transport direction, wherein the
detection unit detects whether the leading end of the recording
medium passes through the gap by detecting movement of the contact
member.
5. The image forming apparatus according to claim 4, wherein the
contact member covers an upstream part of the trailing end holding
member in the transport direction.
6. The image forming apparatus according to claim 1, wherein the
stopping unit stops rotation of the transfer member after rotating
the transfer member in an opposite direction.
7. The image forming apparatus according to claim 1, wherein the
stopping unit stops rotation of the transfer member after the
trailing end holding member rotates downstream in the transport
direction of the recording medium.
8. An image forming apparatus comprising: an image carrier that
carries an image on an outer peripheral surface thereof; a transfer
member disposed such that an outer peripheral surface thereof is in
contact with the outer peripheral surface of the image carrier, the
transfer member transporting a recording medium, the transfer
member transferring the image carried by the image carrier to the
recording medium; a leading end holding member disposed on the
transfer member and holding a leading end of the recording medium
in a transport direction; a trailing end holding member disposed at
a predetermined standby position, the trailing end holding member
being rotatable around the transfer member independently of the
transfer member, the trailing end holding member holding a trailing
end of the recording medium in the transport direction after the
leading end of the recording medium is held by the leading end
holding member while the transfer member rotates; a detection unit
that detects a position of the trailing end holding member; and a
stopping unit that stops rotation of the transfer member when the
detection unit detects that the trailing end holding member is not
positioned at the standby position before the trailing end holding
member holds the trailing end.
9. The image forming apparatus according to claim 8, wherein the
trailing end holding member is movable by a force applied to the
trailing end holding member in the transport direction.
10. The image forming apparatus according to claim 8, wherein the
stopping unit stops rotation of the transfer member after rotating
the transfer member in an opposite direction.
11. The image forming apparatus according to claim 8, wherein the
stopping unit stops rotation of the transfer member after the
trailing end holding member rotates downstream in the transport
direction of the recording medium.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based on and claims priority under 35
USC 119 from Japanese Patent Application No. 2012-037709 filed Feb.
23, 2012.
BACKGROUND
Technical Field
[0002] The present invention relates to an image forming
apparatus.
SUMMARY
[0003] According to an aspect of the invention, an image forming
apparatus includes an image carrier, a transfer member, a leading
end holding member, a trailing end holding member, a detection
unit, and a stopping unit. The image carrier carries an image on an
outer peripheral surface thereof. The transfer member is disposed
such that an outer peripheral surface thereof is in contact with
the outer peripheral surface of the image carrier. The transfer
member transports a recording medium and transfers the image
carried by the image carrier to the recording medium. The leading
end holding member is disposed on the transfer member and holds a
leading end of the recording medium in a transport direction. The
trailing end holding member is disposed at a predetermined standby
position such that a gap is formed between the trailing end holding
member and the outer peripheral surface of the transfer member. The
trailing end holding member is rotatable around the transfer member
independently of the transfer member. The trailing end holding
member holds a trailing end of the recording medium in the
transport direction after the leading end of the recording medium
in the transport direction held by the leading end holding member
has passed through the gap while the transfer member rotates. The
detection unit detects whether the leading end of the recording
medium passes through the gap after the leading end holding member
performed a holding operation on the leading end. The stopping unit
stops rotation of the transfer member when the detection unit
detects that the leading end does not pass through the gap.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] Exemplary embodiments of the present invention will be
described in detail based on the following figures, wherein:
[0005] FIG. 1 is a schematic view illustrating the structure of an
image forming apparatus;
[0006] FIGS. 2A and 2B are schematic views illustrating the
structure of a transfer device;
[0007] FIGS. 3A to 3C illustrate an image forming operation;
[0008] FIGS. 4A to 4C illustrate the image forming operation;
[0009] FIGS. 5A and 5B illustrate the image forming operation;
[0010] FIG. 6 is a schematic view illustrating the structure of a
transfer device according to another exemplary embodiment;
[0011] FIGS. 7A and 7B are schematic views illustrating a
modification of the transfer device illustrated in FIG. 6;
[0012] FIGS. 8A and 8B are schematic views illustrating a
modification of the transfer device illustrated in FIGS. 7A and
7B;
[0013] FIGS. 9A and 9B are schematic views illustrating a
modification of the transfer device illustrated in FIGS. 2A and 2B;
and
[0014] FIGS. 10A and 10B are schematic vies illustrating a
modification of the transfer devices illustrates FIGS. 2A, 2B, 7A,
and 7B.
DETAILED DESCRIPTION
[0015] Hereinafter, an exemplary embodiment of the present
invention will be described with reference to the drawings.
[0016] Structure of Image Forming Apparatus According to Present
Exemplary Embodiment
[0017] First, the structure of an image forming apparatus according
to the present exemplary embodiment will be described. FIG. 1 is a
schematic view illustrating the structure of an image forming
apparatus 50 according to the present exemplary embodiment.
[0018] As illustrated in FIG. 1, the image forming apparatus 50
includes an image forming apparatus body 62 and various components
disposed in the image forming apparatus body 62. An image forming
unit 10, a recording medium feeder 40, and a controller 60 are
disposed in the image forming apparatus body 62. The image forming
unit 10 forms an image on a recording medium P, which is an example
of a transported object. The recording medium feeder 40 feeds the
recording medium P to the image forming unit 10. The controller 60
controls the operation of each component of the image forming
apparatus 50. A recording medium output unit 63 is disposed on an
upper part of the image forming apparatus body 62. After an image
has been formed on the recording medium P by the image forming unit
10, the recording medium P is output to the recording medium output
unit 63.
[0019] The recording medium feeder 40 includes a recording medium
container 41 and a transport unit 45. The recording medium
container 41 contains the recording medium P. The transport unit 45
transports the recording medium P from the recording medium
container 41 to the image forming unit 10. The transport unit 45
includes a feed roller 42 and plural transport rollers 44. The feed
roller 42 feeds the recording medium P contained in the recording
medium container 41. The transport rollers 44 are arranged along a
transport path 51 of the recording medium P and transport the
recording medium P, which has been fed by the feed roller 42, to
the image forming unit 10.
[0020] The image forming unit 10 includes a photoconductor drum 11
and a transfer device 20. The photoconductor drum 11 is an example
of an image carrier that carries an image. The transfer device 20
transfers the image (toner image), which is carried by the
photoconductor drum 11, to the recording medium P. The
photoconductor drum 11 rotates in one direction (for example, the
direction of arrow A in FIG. 1).
[0021] A charging roller 12, an exposure device 13, a rotary
developing device 14, and a cleaner 15 are arranged around the
photoconductor drum 11 in the rotation direction of the
photoconductor drum 11. The charging roller 12, which is an example
of a charger, charges the photoconductor drum 11. The exposure
device 13 exposes the photoconductor drum 11, which has been
charged by the charging roller 12, with light, and thereby forms an
electrostatic latent image on the photoconductor drum 11. The
rotary developing device 14, which is an example of a developing
device, develops the electrostatic latent image, which has been
formed on the photoconductor drum 11 by the exposure device 13, and
thereby forms a toner image. The cleaner 15 cleans residual toner
(developer) remaining on the photoconductor drum 11.
[0022] The exposure device 13 forms an electrostatic latent image
on the basis of an image signal sent from the controller 60.
Examples of an image signal sent from the controller 60 include an
image signal received by the controller 60 from an external
apparatus.
[0023] The rotary developing device 14 includes a rotation shaft
14A; and developing units 14Y, 14M, 14C, and 14K for yellow (Y),
magenta (M), cyan (C), and black (K), which are arranged around the
rotation shaft 14A in the circumferential direction of the rotation
shaft 14A. The rotary developing device 14 rotates around the
rotation shaft 14A in the direction of arrow C. When one of the
developing units 14Y, 14M, 14C, and 14K of the rotary developing
device 14 is located at a facing position at which the developing
unit faces the photoconductor drum 11, an electrostatic latent
image formed on the photoconductor drum 11 is developed by using a
color toner corresponding to the developing unit located at the
facing position, and thereby a toner image is formed.
[0024] The transfer device 20 includes a transfer drum 21 that is
disposed such that the outer peripheral surface of the transfer
drum 21 is in contact with the outer peripheral surface of the
photoconductor drum 11. The transfer drum 21 transfers an image
that is carried by the photoconductor drum 11 to the recording
medium P. The transfer drum 21 is an example of a transfer member.
In the transfer device 20, the recording medium P, which has been
transported by the transport unit 45, is wound around the outer
peripheral surface of the transfer drum 21 (to be specific, the
outer peripheral surface of an elastic layer 21B described below),
and rotates together with the photoconductor drum 11. As a result,
the recording medium P is transported to a transfer position Tr
(transfer region) between the transfer drum 21 and the
photoconductor drum 11, and the transfer drum 21 transfers a toner
image from the photoconductor drum 11 to the recording medium P. As
described below, a leading end gripper 23 and a trailing end
gripper 27 respectively grip the leading end and the trailing end
of the recording medium P in the transport direction, and thereby
the recording medium P is wound around the outer peripheral surface
of the transfer drum 21.
[0025] The recording medium P is supplied to the transfer drum 21
at a supply position Pa shown in FIG. 1 (a holding-start position
at which the leading end gripper 23 (described below) starts
holding the recording medium P). The recording medium P is peeled
off the transfer drum 21 at a peel-off position Pb shown in FIG. 1
(a holding-finish position at which the leading end gripper 23
finishes holding the recording medium P). The structure of the
transfer device 20 will be described below in detail.
[0026] A fixing unit 30 is disposed downstream of (in FIG. 1,
above) the transfer position Tr along the transport path 51. The
fixing unit 30 fixes the toner image, which has been transferred to
the recording medium P by the transfer device 20, to the recording
medium P. The fixing unit 30 includes a heating roller 31 and a
pressing roller 32. The heating roller 31 heats the toner image on
the recording medium P. The pressing roller 32 presses the
recording medium P as a result of being pressed against the heating
roller 31.
[0027] In the fixing unit 30, the recording medium P is pressed and
heated by the pressing roller 32 and the heating roller 31, which
rotate with the recording medium P therebetween while transporting
the recording medium P downstream (in FIG. 1, upward) along the
transport path 51. As a result, the toner image is fixed to the
recording medium P.
[0028] Output rollers 46 are disposed downstream of the fixing unit
30 along the transport path 51.
[0029] The output rollers 46 output the recording medium P, to
which the toner image has been fixed, to the recording medium
output unit 63.
Structure of Transfer Device 20
[0030] Next, the structure of the transfer device 20 will be
described.
[0031] As illustrated in FIG. 1, the transfer device 20 includes
the transfer drum 21, the leading end gripper 23, and the trailing
end gripper 27. The leading end gripper 23, which is an example of
a leading end holding member, is disposed on the transfer drum 21
and grips the leading end of the recording medium P in the
transport direction. The trailing end gripper 27, which is an
example of a trailing end holding member, is disposed on the
transfer drum 21 and grips the trailing end of the recording medium
P in the transport direction.
[0032] A detection sensor 25 for detecting passage of the recording
medium P is disposed so as to face the outer peripheral surface of
the transfer drum 21. The detection sensor 25 is disposed upstream
of a standby position (described below) of the trailing end gripper
27 (the position of the trailing end gripper 27 shown in FIG. 1) in
the transport direction of the recording medium P and on the
transport path along which the recording medium P, which has been
fed from the recording medium container 41, passes.
Transfer Drum 21
[0033] As illustrated in FIG. 1, the transfer drum 21 is disposed
in the image forming apparatus body 62 so as to face the
photoconductor drum 11 and so as to be rotatable around a rotation
shaft 21D. The rotation shaft 21D is rotated by a drive motor 19
that is controlled by the controller 60, and thereby the transfer
drum 21 rotates.
[0034] The transfer drum 21 includes a base member 21A having a
cylindrical shape and the elastic layer 21B formed on the outer
peripheral surface of the base member 21A. The base member 21A is
electroconductive and is made of, for example, a metal material.
The elastic layer 21B is made of a semi-conductive elastic material
(for example, a resin material such as a polyurethane resin).
[0035] The transfer drum 21 rotates in the direction of arrow B in
synchronism with the rotation of the photoconductor drum 11 while
the elastic layer 21B is in contact with the photoconductor drum
11. A part of the elastic layer 21B that contacts the
photoconductor drum 11 becomes elastically deformed.
[0036] A voltage (transfer bias) having a polarity opposite to that
of toner is applied to the base member 21A of the transfer drum 21,
and thereby a toner image is transferred from the photoconductor
drum 11 to the recording medium P, which is wound around the
elastic layer 21B, at the transfer position Tr.
[0037] A portion of the outer peripheral surface of the base member
21A in the circumferential direction is not covered with the
elastic layer 21B. This portion, on which the elastic layer 21B is
not disposed, will be referred to as a cutout portion 21C. That is,
the cutout portion 21C, which is an example of a recess, is formed
in the outer peripheral surface of the transfer drum 21. Even when
the outer peripheral surface of the base member 21A in the cutout
portion 21C faces the photoconductor drum 11, the outer peripheral
surface does not contact the photoconductor drum 11. A
non-conductive layer or the like may be formed on the outer
peripheral surface of the base member 21A in the cutout portion
21C.
[0038] In FIG. 1, the outer periphery of the transfer drum 21 when
the elastic layer 21B is elastically deformed is shown by two-dot
chain line K. For clarity, the two-dot chain line K is drawn around
the entire circumference of the transfer drum 21.
Leading End Gripper 23
[0039] As illustrated in FIG. 1, the leading end gripper 23 is
disposed in the cutout portion 21C of the transfer drum 21. The
leading end gripper 23 rotates together with the transfer drum
21.
[0040] The leading end gripper 23 is rotatably supported by the
transfer drum 21 (to be specific, the base member 21A) at a base
end (a downstream end in the rotation direction of the transfer
drum 21) of the leading end gripper 23. A tip end (an upstream end
in the rotation direction of the transfer drum 21) of the leading
end gripper 23 is capable of contacting and becoming separated from
the outer peripheral surface of the transfer drum 21.
[0041] When the leading end gripper 23 rotates around the base end
in a direction so that the tip end is separated from the outer
peripheral surface of the transfer drum 21, the recording medium P
may enter a space between the tip end and the outer peripheral
surface of the transfer drum 21. When the leading end gripper 23
rotates around the base end in the opposite direction, the leading
end gripper 23 holds the recording medium P between the tip end and
the outer peripheral surface of the transfer drum 21.
[0042] The leading end gripper 23 has a plate-like shape extending
in the axial direction of the transfer drum 21. The length of the
leading end gripper 23 in the axial direction is larger than the
maximum width of the recording medium P, which is wound around the
transfer drum 21, in the axial direction of the transfer drum
21.
[0043] When the leading end gripper 23 is holding the recording
medium P, the leading end gripper 23 is capable of passing the
transfer position Tr without contacting the photoconductor drum 11.
That is, when the leading end gripper 23 is holding the recording
medium P, the leading end gripper 23 is located inside of the
two-dot chain line K in FIG. 1.
[0044] Trailing End Gripper 27
[0045] As illustrated in FIG. 1, the trailing end gripper 27
straddles the outer peripheral surface of the transfer drum 21 in
the axial direction of the transfer drum 21. The trailing end
gripper 27 is supported by support portions 27A disposed at ends of
the transfer drum 21 in the axial direction so that the trailing
end gripper 27 is capable of contacting and becoming separated from
the outer peripheral surface of the transfer drum 21. When the
trailing end gripper 27 is separated from the outer peripheral
surface of the transfer drum 21, there is a space S between the
trailing end gripper 27 and the outer peripheral surface of the
transfer drum 21.
[0046] The support portions 27A are rotatably supported by a
rotation shaft 27D that is coaxial with the rotation shaft 21D of
the transfer drum 21. The rotation shaft 27D is rotated by a drive
motor 29 controlled by the controller 60. As a result, the trailing
end gripper 27 rotates around (the outer periphery of) the transfer
drum 21 independently of the transfer drum 21.
[0047] Before the trailing end gripper 27 grips the recording
medium P, the trailing end gripper 27 is located at a predetermined
standby position (the position of the trailing end gripper 27
illustrated in FIG. 1) on the rotation path of the trailing end
gripper 27. The standby position is, for example, a position on the
transport path 51 between the transfer position Tr (transfer
region) and the supply position Pa in the rotation direction of the
transfer drum 21.
[0048] The trailing end gripper 27 is made of a resin material
(such as PET, a polyimide resin, or a fluorocarbon resin) and has a
plate-like shape (film-like shape) extending in the axial direction
of the transfer drum 21. The length of the trailing end gripper 27
in the axial direction is larger than the maximum width of the
recording medium P (in the axial direction of the transfer drum
21), which is wound around the transfer drum 21. Alternatively, the
trailing end gripper 27 may have a wire-like shape, a solid
cylindrical shape, or the like.
[0049] When the detection sensor 25 detects passage of the trailing
end of the recording medium P in the transport direction, the
trailing end gripper 27 moves from a position in which the trailing
end gripper 27 is separated from the transfer drum 21 to a position
in which the trailing end gripper 27 contacts the transfer drum 21,
and thereby holds the trailing end of the recording medium P by
gripping the trailing end between the trailing end gripper 27 and
the outer peripheral surface of the transfer drum 21 (to be
specific, the outer peripheral surface of the elastic layer
21B).
[0050] As heretofore described, the leading end gripper 23 and the
trailing end gripper 27 respectively grip the leading end and the
trailing end of the recording medium P in the transport direction,
and thereby the recording medium P is wound around the outer
peripheral surface of the transfer drum 21.
Structure for Detecting that Leading End of Recording Medium in
Transport Direction has Risen
[0051] As illustrated in FIG. 2A, the transfer device 20 includes a
detection sensor 70, which is an example of a detection unit. The
detection sensor 70 detects that the leading end of the recording
medium P in the transport direction has risen from the outer
peripheral surface of the transfer drum 21 over the space S when
the leading end was about to pass through the space S after the
leading end gripper 23 performed a holding operation on the leading
end.
[0052] To be specific, the detection sensor 70 detects whether the
trailing end gripper 27, which is to be located at the standby
position, has moved from the standby position. The trailing end
gripper 27 is movable by a pressing force applied to the trailing
end gripper 27 by the recording medium P whose leading end in the
transport direction has risen from the outer peripheral surface of
the transfer drum 21 over the space S.
[0053] To be specific, the trailing end gripper 27 is movable by
using, for example, the following mechanism: a one-way clutch or a
ratchet is disposed in the rotation shaft 27D of the trailing end
gripper 27; a driving force of the drive motor 29 is transmitted to
the rotation shaft 27D of the trailing end gripper 27 through the
one-way clutch or the ratchet; and the rotation shaft 27D of the
trailing end gripper 27 is rotated when the trailing end gripper 27
receives an external force. A stepping motor may be used as the
drive motor 29. In this case, the trailing end gripper 27 may be
moved by an external force generated when the stepping motor loses
synchronism.
[0054] Thus, in the present exemplary embodiment, the trailing end
gripper 27 is movable by a pressing force applied to the trailing
end gripper by the recording medium P whose leading end in the
transport direction has risen from the outer peripheral surface of
the transfer drum 21. When the detection sensor 70 detects that the
trailing end gripper 27 has moved from the standby position, it is
determined that the leading end of the recording medium P in the
transport direction on which the leading end gripper 23 performed a
holding operation has risen from the outer peripheral surface of
the transfer drum 21.
[0055] The detection sensor 70 is, for example, an optical sensor
that emits light from the outer periphery of the trailing end
gripper 27 (from a side farther from the transfer drum 21) toward
the trailing end gripper 27 (or the support portions 27A). In this
case, the detection sensor 70 detects movement of the trailing end
gripper 27 by receiving reflected light reflected from the trailing
end gripper 27 (or one of the support portions 27A) or the
recording medium P (or the outer peripheral surface of the transfer
drum 21) and by measuring a change in the intensity of the
reflected light.
[0056] Alternatively, the detection sensor 70 may be an optical
sensor (for example, a transmissive or reflective optical sensor)
that detects movement of the trailing end gripper 27 by emitting
light in the axial direction of the transfer drum 21. As a further
alternative, the detection sensor 70 may be a switch that connects
or interrupts an electric circuit when the trailing end gripper 27
moves.
[0057] When the detection sensor 70 detects movement of the
trailing end gripper 27, a detection signal is sent to the
controller 60. Then, the controller 60 controls driving of the
drive motor 19 so as to stop rotation of the transfer drum 21. That
is, the controller 60 functions as an example of a stopping unit
that stops rotation of the transfer drum 21.
Operation According to Present Exemplary Embodiment
[0058] Next, an operation according to the present exemplary
embodiment, with which the image forming apparatus 50 forms a toner
image on a recording medium P, will be described.
[0059] As illustrated in FIG. 3A, before an image forming operation
is started, the leading end gripper 23 is located at a standby
position between the transfer position Tr and the supply position
Pa in the rotation direction of the transfer drum 21. The trailing
end gripper 27 is located at the standby position, which is located
between the transfer position Tr and the supply position Pa. The
standby position of the trailing end gripper 27 is upstream of the
standby position of the leading end gripper 23 in the rotation
direction of the transfer drum 21.
[0060] When the image forming operation is started, the feed roller
42 feeds the recording medium P from the recording medium container
41, and the transport rollers 44 transport the recording medium P
toward the transfer drum 21. As illustrated in FIG. 3B, while the
recording medium P is transported toward the transfer drum 21, the
transfer drum 21 rotates and the leading end gripper 23 moves from
the standby position toward the supply position Pa. The transfer
drum 21 is rotated by the drive motor 19 controlled by the
controller 60 (see FIG. 1).
[0061] As illustrated in FIG. 3C, when the recording medium P has
been transported to the transfer drum 21 by the transport rollers
44, the leading end gripper 23 grips the leading end of the
recording medium P in the transport direction at the supply
position Pa. As illustrated in FIG. 4A, while the transfer drum 21
rotates, the leading end of the recording medium P in the transport
direction, which is gripped by the leading end gripper 23, passes
through the space S between the transfer drum 21 and the trailing
end gripper 27 located at the standby position. AS illustrated in
FIG. 4B, when the detection sensor 25 (see FIG. 1) detects passage
of the trailing end of the recording medium P in the transport
direction after the leading end of the recording medium P in the
transport direction has passed through the space S, the trailing
end gripper 27 grips the trailing end of the recording medium P in
the transport direction. Thus, the leading end gripper 23 and the
trailing end gripper 27 respectively grip the leading end and the
trailing end of the recording medium P in the transport direction,
and thereby the recording medium P is wound around the outer
peripheral surface of the transfer drum 21.
[0062] As illustrated in FIG. 4C, the transfer drum 21 and the
trailing end gripper 27 rotate in synchronism with each other while
the recording medium P is wound around the outer peripheral surface
of the transfer drum 21, and thereby the recording medium P is
rotated. Thus, the recording medium P is transported to the
transfer position Tr. The trailing end gripper 27 is rotated by the
drive motor 29 controlled by the controller 60 (see FIG. 1).
[0063] In the image forming unit 10 (see FIG. 1), the
photoconductor drum 11 is charged by the charging roller 12
(charging) and exposed to light by the exposure device 13
(exposure), and thereby an electrostatic latent image is formed on
the photoconductor drum 11. The electrostatic latent image is
developed by the developing unit 14Y that faces the photoconductor
drum 11, and thereby a yellow toner image is formed on the
photoconductor drum 11 (development). The yellow toner image is
transferred by the transfer drum 21 to the recording medium P,
which has been transported to the transfer position Tr.
[0064] The transfer drum 21 and the trailing end gripper 27 rotate
in synchronism with each other, and thereby rotate the recording
medium P. The rotary developing device 14 rotates to a position at
which the developing unit 14M faces the photoconductor drum 11.
Charging, exposure, and development are performed as described
above to form a magenta toner image on the photoconductor drum 11.
The magenta toner image is transferred to the recording medium P,
which is transported to the transfer position Tr again while the
transfer drum 21 and the trailing end gripper 27 rotate. Likewise,
cyan (C) and black (K) toner images are successively transferred to
the recording medium P in an overlapping manner.
[0065] As illustrated in FIG. 5A, after the toner images have been
transferred to the recording medium P in an overlapping manner, the
leading end gripper 23 releases the leading end of the recording
medium P in the transport direction at the peel-off position Pb,
and thereby the recording medium P is peeled off the transfer drum
21.
[0066] As illustrated in FIG. 5B, the trailing end gripper 27
rotates to the standby position and releases the trailing end of
the recording medium P in the transport direction and then waits at
the standby position. The leading end gripper 23 rotates to the
standby position together with the transfer drum 21 and waits at
the standby position.
[0067] The recording medium P, which has been peeled off the
transfer drum 21, is transported to the fixing unit 30, and the
toner images are fixed to the recording medium P by the fixing unit
30. The recording medium P, on which the toner images have been
fixed, is output to the recording medium output unit 63 by the
output rollers 46. An image forming process is performed as
heretofore described.
[0068] FIG. 2B illustrates a case where the leading end of the
recording medium P in the transport direction has risen from the
outer peripheral surface of the transfer drum 21 over the space S
when the leading end was about to pass through the space S after
the leading end gripper 23 performed a holding operation (see FIG.
3C) on the leading end. In this case, with the present exemplary
embodiment, the leading end in the transport direction, which has
risen, contacts the trailing end gripper 27 and presses the
trailing end gripper 27 downstream in the rotation direction
(toward the transfer position Tr). Thus, the trailing end gripper
27 moves downstream in the rotation direction.
[0069] The leading end of the recording medium P in the transport
direction may rise from the outer peripheral surface of the
transfer drum 21 over the space S if, for example, the leading end
gripper 23 insufficiently grips the recording medium P and thereby
a part of the recording medium P in the width direction (the axial
direction of the transfer drum 21) that is located upstream of the
standby position of the trailing end gripper 27 rises from the
outer peripheral surface.
[0070] If the trailing end gripper 27 moves downstream in the
rotation direction, the detection sensor 70 detects that the
trailing end gripper 27 has moved from the standby position. The
detection sensor 70 sends a detection signal indicating the
movement of the trailing end gripper 27 to the controller 60. When
the controller 60 receives the detection signal, the controller 60
controls the drive motor 19 so as to stop rotation of the transfer
drum 21, and the rotation of the transfer drum 21 is stopped. Thus,
the trailing end gripper 27 is prevented from being damaged because
rotation of the transfer drum 21 is stopped if the trailing end
gripper 27 is pressed by the recording medium P and a load is
applied to the trailing end gripper 27. When the rotation of the
transfer drum 21 is stopped, driving (rotation) of the
photoconductor drum 11 and driving (rotation) of the transport unit
45 (the feed roller 42 and the transport rollers 44) are
stopped.
[0071] With the present exemplary embodiment, the trailing end
gripper 27 moves if the trailing end gripper 27 is pressed by the
recording medium P whose leading end in the transport direction has
risen from the outer peripheral surface of the transfer drum 21.
Therefore, a force applied to the trailing end gripper 27 by the
recording medium P is reduced, and thereby the trailing end gripper
27 is prevented from being damaged.
[0072] With the present exemplary embodiment, rotation of the
transfer drum 21 is stopped when a load is actually applied to the
trailing end gripper 27. Therefore, it is less likely that rotation
of the transfer drum 21 is unnecessarily stopped than in a case
where a detector directly detects the recording medium P whose
leading end in the transport direction has risen from the outer
peripheral surface of the transfer drum 21. In contrast, in a case
where a sensor directly detects the recording medium P whose
leading end in the transport direction has risen from the outer
peripheral surface of the transfer drum 21, if the accuracy of
detection is low, rotation of the transfer drum 21 may be stopped
even if a load is not actually applied to the trailing end gripper
27.
Another Embodiment of Transfer Device 20
[0073] The image forming apparatus 50 may include a transfer device
120 instead of the transfer device 20. Hereinafter, the transfer
device 120 will be described. Only the difference between the
transfer device 120 and the transfer device 20 will be described,
and components of the transfer device 120 having the same functions
as those of the transfer device 20 will be denoted by the same
numerals and the description of such components will be
omitted.
[0074] As illustrated in FIG. 6, the transfer device 120 includes a
contact member 80 that is disposed upstream of the standby position
of the trailing end gripper 27 in the transport direction of the
recording medium P. The contact member 80 contacts the recording
medium P whose leading end in the transport direction has risen
from the outer peripheral surface of the transfer drum 21 over the
space S. The contact member 80 is disposed in the image forming
apparatus body 62 so as to be movable by a pressing force applied
to the contact member 80 by the recording medium P whose leading
end in the transport direction has risen from the outer peripheral
surface of the transfer drum 21 over the space S.
[0075] To be specific, the contact member 80 is disposed in the
image forming apparatus body 62 so as to be independent of the
transfer drum 21 and the trailing end gripper 27. That is, the
contact member 80 is not connected to the transfer drum 21 and the
trailing end gripper 27 but is directly or indirectly attached to
the image forming apparatus body 62.
[0076] The contact member 80 also serves as a protection member
that covers, without contacting, an upstream part (a lower end part
in FIG. 6) of the trailing end gripper 27 in the transport
direction of the recording medium P. The contact member 80, serving
as a protection member, protects the trailing end gripper 27
against the recording medium P whose leading end in the transport
direction has risen from the outer peripheral surface of the
transfer drum 21 over the space S.
[0077] The transfer device 120 includes a detection sensor 170
instead of the detection sensor 70. The detection sensor 170, which
is an example of a detection unit, detects movement of the contact
member 80. That is, with the transfer device 120, the detection
sensor 170 detects that the leading end of the recording medium P
in the transport direction on which the leading end gripper 23
performed a holding operation has risen from the outer peripheral
surface of the transfer drum 21 over the space S by detecting that
the contact member 80 has independently moved from the standby
position.
[0078] As with the detection sensor 70, the detection sensor 170
is, for example, an optical sensor that emits light from an outer
periphery of the contact member 80 (from a side farther from the
transfer drum 21) toward the contact member 80. In this case, the
detection sensor 170 detects movement of the contact member 80 by
receiving reflected light reflected from the contact member 80 or
the outer peripheral surface of the transfer drum 21 and by
measuring a change in the intensity of the reflected light.
[0079] Alternatively, the detection sensor 170 may be an optical
sensor (for example, a transmissive or reflective optical sensor)
that detects movement of the contact member 80 by emitting light in
the axial direction of the transfer drum 21. As a further
alternative, the detection sensor 170 may be a switch that connects
and breaks an electric circuit when the contact member 80
moves.
[0080] When the detection sensor 170 detects movement of the
contact member 80, a detection signal is sent to the controller 60.
Then, the controller 60 controls driving of the drive motor 19 so
as to stop rotation of the transfer drum 21.
[0081] FIG. 6 illustrates a case where the leading end of the
recording medium P in the transport direction has risen from the
outer peripheral surface of the transfer drum 21 over the space S
when the leading end was about to pass through the space S after
the leading end gripper performed a holding operation (see FIG. 3C)
on the leading end. In this case, with the transfer device 120, the
leading end in the transport direction, which has risen, contacts
the contact member 80 and presses the contact member 80 downstream
in the rotation direction (toward the transfer position Tr). Thus,
the contact member 80 moves downstream in the rotation
direction.
[0082] If the contact member 80 moves downstream in the rotation
direction, the detection sensor 170 detects the movement of the
contact member 80. The detection sensor 170 sends a detection
signal indicating the movement of the contact member 80 to the
controller 60. Then, the controller 60 controls the drive motor 19
so as to stop rotation of the transfer drum 21, and the rotation of
the transfer drum 21 is stopped.
[0083] Thus, the transfer device 120 detects that the leading end
of the recording medium P in the transport direction has risen from
the outer peripheral surface of the transfer drum 21 before the
recording medium P contacts the trailing end gripper 27. That is,
before a load is applied to the trailing end gripper 27 by the
recording medium P, the transfer device 120 detects that the
leading end of the recording medium P in the transport direction
has risen. As a result, the trailing end gripper 27 is more
effectively prevented from being damaged.
[0084] Moreover, because the contact member 80 of the transfer
device 120 also functions as a protection member, the trailing end
gripper 27 is more effectively prevented from being damaged.
[0085] The contact member 80 may be in contact with the trailing
end gripper 27, and the contact member 80 may be moved together
with the trailing end gripper 27 when the contact member 80 is
pressed by the recording medium P whose leading end has risen from
the outer peripheral surface of the transfer drum 21.
Modifications of Transfer Device 120
[0086] As illustrated in FIG. 7A, at least a part of the contact
member 80 may be disposed over the outer periphery of the trailing
end gripper 27 so as to be located upstream of the standby position
of the trailing end gripper 27 in the transport direction of the
recording medium P.
[0087] Alternatively, as illustrated in FIG. 7B, the contact member
80 may cover the outer periphery of the trailing end gripper 27 in
addition to the upstream part of the trailing end gripper 27 in the
transport direction of the recording medium P (the lower end part
in FIG. 7B).
[0088] As a further alternative, as illustrated in FIG. 8A, at
least a part the contact member 80 may be disposed over the inner
periphery of the trailing end gripper 27 so as to be located
upstream of the standby position of the trailing end gripper 27 in
the transport direction of the recording medium P.
[0089] In the case where the contact member 80 is disposed over the
inner periphery of the trailing end gripper 27, as illustrated in
FIG. 8B, for example, a cutout portion (not shown) is formed in at
least one of the contact member 80 and the trailing end gripper 27
so as to allow the trailing end gripper 27 to pass through the
contact member 80 when the trailing end gripper 27 moves so as to
contact and become separated from the outer peripheral surface of
the transfer drum 21.
Modifications of Transfer Devices 20 and 120
[0090] With the transfer device 20, when the controller 60 receives
a detection signal from the detection sensor 70, the controller 60
simply controls the drive motor 19 so as to stop rotation of the
transfer drum 21. However, as illustrated in FIG. 9A, the
controller 60 may control the drive motor 19 so that rotation of
the transfer drum 21 is stopped after transporting the recording
medium P in a direction opposite to the transport direction by
reversely rotating the transfer drum 21. With this modification,
rotation of the transfer drum 21 is stopped after the trailing end
gripper 27 has been relieved of a load applied by the recording
medium P whose leading end in the transport direction has risen
from the outer peripheral surface of the transfer drum 21. The
modification illustrated in FIG. 9A is applicable not only to the
transfer device 20 but also to the transfer device 120.
[0091] In addition to or instead of the modification illustrated in
FIG. 9A, as illustrated in FIG. 9B, the controller 60 may control
the drive motor 19 so that rotation of the transfer drum 21 is
stopped after the trailing end gripper 27 rotates downstream in the
transport direction of the recording medium P. With this
modification, rotation of the transfer drum 21 is stopped after the
trailing end gripper 27 has been relieved of a load applied by the
recording medium P whose leading end in the transport direction has
risen from the outer peripheral surface of the transfer drum 21.
The modification illustrated in FIG. 9B is applicable not only to
the transfer device 20 but also to the transfer device 120.
[0092] Ease of motion (movement resistance) of the trailing end
gripper 27 of the transfer device 20 and the contact member 80 of
the transfer device 120 may be variable. For example, when forming
an image on a thin recording medium P or when humidity is low, the
movement resistance of the trailing end gripper 27 (or the contact
member 80) may be reduced to increase ease of motion. When forming
an image on a thick recording medium P or on an envelope, the
movement resistance of the trailing end gripper 27 (or the contact
member 80) may be increased to reduce ease of motion. When
transporting a thick recording medium P or an envelope, the
trailing end gripper 27 may receive a load even when such a thick
sheet normally passes through the space S. By changing ease of
motion (movement resistance) as described above, rotation of the
transfer drum 21 is prevented from being unintentionally stopped.
The movement resistance of the trailing end gripper 27 may be
changed by, for example, changing an excitation current applied to
a stepping motor that is used as the drive motor 29.
[0093] The transfer device 20 and the transfer device 120
respectively detect movement of the trailing end gripper 27 and
movement of the contact member 80, and thereby detects that the
leading end of the recording medium P in the transport direction on
which the leading end gripper 23 performed a holding operation has
risen from the outer peripheral surface of the transfer drum 21
over the space S. Instead, as illustrated in FIGS. 10A and 10B, a
detection sensor 270 may be used to directly detect the leading end
of the recording medium P in the transport direction that has risen
from the outer peripheral surface of the transfer drum 21 over the
space S. As illustrated in FIG. 10A, the detection sensor 270 is,
for example, a transmissive optical sensor that includes a light
emitter 270A and a light receiver 270B and detects the leading end
of the recording medium P in the transport direction. The light
emitter 270A is disposed at one end of the transfer drum 21 in the
axial direction and emits light in the axial direction of the
transfer drum 21. The light receiver 270B is disposed at the other
end of the transfer drum 21 in the axial direction. As illustrated
in FIG. 10B, the detection sensor 270 is disposed upstream of the
standby position of the trailing end gripper 27 in the transport
direction of the recording medium P and detects that the leading
end of the recording medium P in the transport direction has risen
from the outer peripheral surface of the transfer drum 21 over the
space S at a position upstream of the standby position in the
transport direction of the recording medium P. The detection sensor
270 may be a reflective optical sensor.
[0094] The present invention is not limited to the exemplary
embodiments described above and may be modified, changed, and
improved in various ways. For example, the modifications described
above may be used in combination.
[0095] The foregoing description of the exemplary embodiments of
the present invention has been provided for the purposes of
illustration and description. It is not intended to be exhaustive
or to limit the invention to the precise forms disclosed.
Obviously, many modifications and variations will be apparent to
practitioners skilled in the art. The embodiments were chosen and
described in order to best explain the principles of the invention
and its practical applications, thereby enabling others skilled in
the art to understand the invention for various embodiments and
with the various modifications as are suited to the particular use
contemplated. It is intended that the scope of the invention be
defined by the following claims and their equivalents.
* * * * *